In line with the Army's continuing efforts to minimize hazards associated with propellant formulations used in its missile systems, a replacement propellant formulation has been sought that reduces some of the hazards associated with ammonium perchlorate propellants that use certain modifiers or additives such as 2,2-bis(ethyldicyclopentadienyliron)propane (also known as the trademark material Catocene) to enhance or increase propellant burn rate. Iron-containing compounds are now the current choice as burn rate enhancers for ammonium perchlorate propellants. Of these iron-containing compounds, ferrocene and its derivatives are the most efficient.
Earlier work with propellants containing solid iron compounds gave inconsistent burn rate enhancement because of the difficulty of getting a homogeneous mixture. Thereafter, liquid iron compounds were sought since it was believed that liquids would be better for mixing purposes. This plan of action lead to the development of bis(ethyldicyclopentadienyliron)methane, registered under Trademark Hycat 6D. Hycat 6D migrated readily within the solid propellant producing unsatisfactory propellant properties. Hycat 6D has a total of six alpha hydrogens (hydrogen adjacent to aromatic ring). It is known that hydrogens adjacent to aromatic ring systems are susceptible to oxidation to form acids and/or hydroperoxides. Hydroperoxides are known to be highly unstable compounds.
Since the alpha hydrogens were believed to be the reason for long term oxidation problems, Catocene was developed by coupling two ethylferrocenes with acetone, thus replacing the two bridged hydrogens with two methyl groups. Catocene then became the choice as a burn rate accelerator for ammonium perchlorate-based propellants. By replacing the two bridged hydrogens with methyl groups, long term oxidation and migration problems were reduced. However, accidental ignitions of solid propellants containing Catocene have occurred in both freshly prepared and aged propellants.
Therefore, the current status of Catocene in light of the concern for safety, where accidental ignition has been a problem for both freshly prepared and aged propellants, has motivated the development of a dicyclopentadienyliron compound that performs at the level of Catocene while having improved safety characteristics.
Therefore, an object of this invention is to provide a solid propellant composition which employs a dicyclopentadienyliron compound as a burn rate enhancer while retaining improved safety characteristics for the propellant formulation as compared with Catocene employed in a similar propellant formulation.